Microwave process and apparatus



June 9, 1964 H. c. ANDERSON ETAL 3,137,003

MICROWAVE PROCESS AND APPARATUS Filed- Dec. 5, 1960 INVENTOR5 f/k rwZd'zirzderswz Xazzzzei e ZZzer;

BY M) ATTORNEYS United States Patent 3,137,003 MICROWAVE PRQCESS ANDAPPARATUS Harold C. Anderson, Silver Spring, and Kenneth E. Peltzer,College Park, Md., assignors to Litton Systems, Inc., College Park, Md.

' Filed Dec. 5, 1960, Ser. No. 73,696

5 Claims. (Cl. 346-44) This invention generally relates to improvementsin ferromagnetic recording'of microwaves and is particularly concernedwith the spectral recording of microwaves in both the space and timedomains.

' It is known that microwave radio beams and even higher frequency radiowaves may be magnetically recorded and stored by a process involvingpremagnetizing certain ferromagnetic materials, such as ferrites, bymeans of a strong static magnetic field having an intensity related tothe frequency to be recorded by the Zeeman energy relationship. Aftersensitizing the ferromagnetic material in this manner, the material isthen subjected directly to the radiated microwave having a magnetic or Hcom-' ponent polarized at right angles to the static field, whereby theintelligence in the wave is recorded by varying the magnetized conditionof the ferromagnetic material.

Although the interaction phenomena between the static eld, microwave,and ferromagnetic material is rather complex and difi'icult to explainin a nonrigorous manner, one general explanation that may aid in anunderstanding of this process is that the magnetic dipoles in thematerial are tuned to the frequency of the wave and polarized by thestatic magnetic field whereby the microwave to be recorded exerts atorque on the dipoles to reorient the spin axes thereof and vary themagnetized condition of that area of the material exposed to the wave.The

extent of this reorientation or the number of dipoles whose axes aredisplaced, is related to the intensity of the microwave whereby anintelligence modulated wave may be recorded as different magneticintensities in the material. In carrying out the process theferromagnetic material may be disposed on a tape or other elongatedrecord member, and the member moved lengthwise past the microwave to berecorded in a manner similar to conventional recording at lowfrequencies to provide a series of intensity modulated magnetic imagesvariable along the length of the record according to the intelligence.For a more rigorous explanation of this phenomena, reference is made toarticles entitled The Nonlinear Behavior of Ferrites at High MicrowaveSignal Levels by Harry Suhl, published in the Proceedings IRE, vol. 44,No. 10, page 1270, October 1956, Radiation Magnetization by C. H.Becker, published in Zeitschrift fiir Physik, Bd. 148, pages 391-401,and dated in 1957, and Magnetic Resonance in Ferrites by NicolasBloembergen, published in the Proceedings IRE, vol. 44, No. 10, page1259, dated October 1956; V 7

According to the present inventiornthere is provided an improvement inthis process wherein the magnetic recording is not only intensitymodulated according to the intelligence of the signal but, in addition,the magnetic recording is also made in the space or frequency domainwith the Various component frequencies contained in the microwave beingrecorded at different positions along the record, thereby providing aspectral frequency image of ice \ quenc'y recording, with the degree ofor intensity of magnetization along the length of themoving record beingvariable according to the time variations in amplitude of the microwave.In the present invention, on the other hand, the modulated microwave tobe recorded may be considered in the Fourier analysis manner as the sumof a series of different frequency components, including the fundamentalor carrier frequency wave together with the different frequencysidebands thereof. By recording these frequency components in the spacedomain, or otherwise stated in the frequency domain, these differentfrequency components making up the Waveform are individually captured orimaged at different spatial positions on the record whereby,for example,the carrier frequency component is recorded at the center of the recordand the upper and lower frequency sidebands thereof are recorded nearopposite sides of the record. The relative amplitudes of these differentfrequency components of the wave are also magnetically distinguishablefrom one another on the record since the number of spin statesreoriented at each position on the record are proportional to'theamplitude of that component of frequency affecting that position on therecord.

As in the prior art processes, the ferromagnetic material may also becoated on or embedded in an elongated tape or other suitable carrierthat is movable past the electromagnetic wave, thereby enabling a timeseries of spectral images of the high frequency wave to be capturedalong the length of the record.

It'is accordingly a principal object of the invention to provide aprocess for ferromagnetically recording microwaves in the space orfrequency, domain.

A further object is to directly record such waves without a magnetictransducer.

A still further object is to provide such a process wherein the spectralfrequency componentsof a microwave are recorded at variable intensitiesaccording to the relative amplitudes of such components.

Still another object is to provide such a process wherein a series ofmagnetic recordings or images of the microwave may be made in timesequence.

. Other objects and additional advantages will be more readilycomprehended by those skilled in the art after'a detailed considerationof the following specification taken with the accompanying drawingswherein:

FIG. 1 is a perspective view illustrating one manner of practicing therecording process according to the invention, and

FIG. 2 is a cross sectional view observed from the left hand side inFIG. 1. p

Referring'now to the drawings for a consideration of oneprocess forapplying the invention, there is shown in FIGS. 1 and 2, an elongatedtape 10 or other record member being comprised of a suitable base havingcoated or impregnated therein a suitable ferromagnetic material, such asone of the known ferrite compositions commonly employed for binarymagnetic memory devices in electronic computers. The record member 10 ispositioned between a pair of opposite polarity magnet poles 11 and 12and may be suitably guided and provided with drive means (not shown) formovement lengthwise between the pole pieces 11 and 12. The magneticpoles 11 and 12 may be either portions of a strong permanent magnetstructure or a suitable electromagnet, in either case the magnet beingcapable of producing a strong static magnetic field 13 through the tapeto premagnetize the ferrite material.

As best shown in FIG. 2, the pole faces 14 and 15 are uniformly inclinedaway from each other to provide a progressively increasing air gapbetween the poles 11 and 12 from right to left transversely across thetape 10. As a result, the magnetic field or flux 13 between the poles 11and 12 and passing through the tape 10, progressively decreases inintensity across the tape with the concentration of flux at the rightside in FIG. 2, and represented by the lines numbered 13b, being fargreater than the fiux density 13a at the left side of the tape, and withthe intermediate portions across the tape receiving a pro gressivelyless intense magnetic field from right to left. As generally discussedabove, the static magnetic field 13 servesto premagneti'ze or tune themagnetic dipoles in the ferromagnetic material, conditioning thesedipoles to respond to a high frequency electromagnetic wave having amagnetic or H component disposed at right angles to the static field 13.The relationship between the resonant frequency response of the dipolesand the static magnetic field is known to be linear according to theZeeman energy relationship. Consequently, those portions at the righthand side of the tape 10 in FIG. 2, that are energizedby the mostintense magnetic field 13b, are tuned to respond to a much higherfrequency wave than those at the left hand side of the tape 10 and theregions therebetween extending from right to left across the tape areprogressively tuned to resonate at microwave frequencies between thehigher and lower frequency.

The electromagnetic wave 17 to be imaged or recorded on the tape 10 ispolarized to excite the tape in such manner that the H or magneticcomponent thereof is at right angles to the static field 13. Thispolarized electromagnetic Wave 17 may be conveyed through a suit ablypositioned waveguide 16 as shown, that is properly designed to transmitthe microwave in the correct mode desired to excite the tape 10.

Due to the fact that the surface of the tape 10 is not equallypremagnetized in a direction transversely thereacross, the differentpositions or regions across the tape are tuned to resonate at differentfrequency radio waves, and consequently a radio wave at one givenfrequency within the tuned range will be recorded at only one trans:verse region on the tape that is tuned to resonate at that frequency.Similarly, a radio wave at a second frequency will be recorded at adifferent transverse region on the tape. Consequently, the variousfrequency sideband components being contained in an intelligencemodulated radio wave 17 will be recorded in a spatially dispersedpattern across the record, to capture a spectral magnetic image of theradio beam transversely across the tape.

As generally mentioned above, the recording phenomena results from thefact that the microwave 17 interacts with the static magnetic field 13to produce a torque on the magnetic dipoles in the ferromagneticmaterial, thereby to reorient the axes thereof and produce a measurablemagnetic change in the material in the regions of the tape affected. Theextent of this change or the degree of magnetization being produced ateach transverse position is proportional to the strength or intensity ofthat frequency component of the microwave 17. Therefore, the relativeamplitudes of the spectral components being recorded at differentpositions are distinguishable from one another by the relative intensityof the magnetic change produced at each different region on the record.In other words, the different component frequencies in the radio waveare magnetically recorded in a spectral or spatial distributiontransversely across the tape 10 with each frequency component producinga 4 magnetic intensity change in the record material corresponding tothe relative amplitude of that frequency component in the wave.

Although but one preferred process for carrying out the invention hasbeen illustrated and described, it is believed evident that many changesmay be made by those skilled in the art without departing from thespirit and scope of the invention. For example, the record member 10 maybe in the form of a drum, sphere, or in any other shape or size desiredaccording to the application of the process. Similarly, the microwave 17to be recorded may be obtained and focussed in any known manner withoutthe need for a specific wave guide structure 16 or other specific typeconveying means. The static magnetic field 13 may be produced bypermanent magnets or electromagnets having any desired pole faceconfiguration or in other known manner to provide any desirednonhomogenous static magnetic field pattern transversely across orlengthwise along the record member, as is desired. Consequently,according to the present invention, the ferromagnetic record may bepremagnetized in any uniform or non uniform spatial pattern as desiredto spectrally record the intelligence in any desired spatial code ascontrolled by the static magnetic field pattern energizing theferromagnetic material.

Since these and many other changes may be made, this invention is to beconsidered as being limited only according to the following claimsappended hereto.

What is claimed is:-

1. A process for magnetically recording a spectrum of the componentfrequencies of a microwave frequency field on a ferromagnetic membercomprising the steps of: producing a spatially variable static magneticfield with the intensities of the field at different positions in spacebeing related to the component frequencies to be recorded by the Ze'emanenergy relationship, subjecting a region of the ferromagnetic materialto the field thereby to premagnetize different positions on the materialto different magnetic intensities, and directing the microwave field toa be recorded simultaneously over the region of the ferromagneticmaterial subjected to the static field, with the H component of themicrowave field being transverse to the static magnetic field.

2. A process for magnetically recording the integral frequencycomponents of a microwave frequency field at different spatial positionson an elongated ferromagnetic material comprising the steps of:producing a nonuniform magnetic field in space in the pattern desired,subjecting a region of the ferromagnetic material to the nonuniformfield with different spaced areas of the ferromagnetic material beingsubjected to different intensities of the magnetic field, and directinga microwave frequency intelligence modulated signal to simultaneouslyexcite an extended region of the ferromagnetic material with the wavebeing polarized so that the H vector thereof is transverse to thenonuniform magnetic field.

3. A process for magnetically recording simultaneously the integralcomponents of a high frequency electromagnetic wave at differentpositions along an extended region of ferromagnetic material, comprisingthe steps of: nonuniformly premagnetizing an extended region of theferrm magnetic material, with the intensity of the premagnetizations atdifferent spaced positions in the region being different and related tothe frequency component to be recorded at that position by the Zeemanenergy relationship, and simultaneously exposing the extended region ofthe premagnetized material to the wave to be recorded that is polarizedin such direction that the H vector thereof is transverse to the staticmagnetic field at each different position in the region. 7

4. A process for magnetically recording a frequency spectrum of theintegral components of a high frequency electromagnetic field along anextended region of ferromagnetic material comprising the steps of:producing a nonuniform static magnetic field along the region of thematerial with the intensity of the static magnetic field proin theregion being related to the frequency component g to be recorded at thatposition .by the Zeeman energy relationship, and simultaneously exposingthe extended region of the material to the field to be recorded, whichmicrowave is polarized in such manner that the H vector thereof istransverse to the static magnetic field at each different positionacross the region.

5. A process for directly recording microwave radio beams comprising thesteps of: dispersing a ferromagnetic material along an extended surface,tuning said material to a range of microwave frequencies that it isdesired to record by energizing said surface with a static magneticfield of nonuniform intensity over said surface related to the range offrequencies to be recorded by the Zeeman energy relationship, andsimultaneously exciting said surfacewith a polarized beam of themicrowave to be recorded with the H vector of the beam being transverseto the static field. 1

' References Cited in the file of this patent Becker Sept. 13, 1960

1. A PROCESS FOR MAGNETICALLY RECORDING A SPECTRUM OF THE COMPONENTFREQUENCIES OF A MICROWAVE FREQUENCY FIELD ON A FERROMAGNETIC MEMBERCOMPRISING THE STEPS OF: PRODUCING A SPATIALLY VARIABLE STATIC MAGNETICFIELD WITH THE INTENSITIES OF THE FIELD AT DIFFERENT POSITIONS IN SPACEBEING RELATED TO THE COMPONENT FREQUENCIES TO BE RECORDED BY THE ZEEMANENERGY RELATIONSHIP, SUBJECTING A REGION OF THE FERROMAGNETIC MATERIALTO THE FIELD THEREBY TO PREMAGNETIZE DIFFERENT POSITIONS ON THE MATERIALTO DIFFERENT MAGNETIC INTENSITIES, AND DIRECTING THE MICROWAVE FIELD TOBE RECORDED SIMULTANEOUSLY OVER THE REGION OF THE FERROMAGNETIC MATERIALSUBJECTED TO THE STATIC FIELD, WITH THE H COMPONENT OF THE MICROWAVEFIELD BEING TRANSVERSE TO THE STATIC MAGNETIC FIELD.